1. Field of the Invention
This invention concerns the seal material for lamps, such as xenon lamps and halogen lamps.
2. Description of Related Art
Functionally gradient materials are composed of mixed sinters of, for example, an electrically conductive material, such as a metal, and a non-conductive material, such as an oxidation product of a metal. By varying the proportion of the conductive material in stages in a specified direction, it is possible to form a material that has a conductive portion where there is a high proportion of the conductive material as well as a non-conductive portion where there is a low proportion of the conductive material. The conductive and non-conductive portions make up a solid whole that is well-suited as a seal material that forms a current feed in lamp seals.
When this sort of functionally gradient material is used as a lamp seal, it is necessary for the electrical feed lead bar to pass through the functionally gradient material in order to provide electrical contact between the inside and outside of the lamp. For example, it is possible to make a through-hole for the lead bar from the end of the functionally gradient material in the direction of the build-up, or to make non-through lead bar holes in each end of the functionally gradient material and insert the lead bar into one of the holes.
With such functionally gradient materials, if a tungsten lead bar is attached as within the functionally gradient material, the lead bar and the functionally gradient material will be attached even in the region of the functionally gradient material where there is a high proportion of non-conductive material. Thus, cracking sometimes occurs in the post-sintering cooling stage of the process of manufacturing the functionally gradient material, due to the different indices of thermal expansion of the tungsten and the non-conductive material.
Methods to solve the problem described above have been proposed, including the method of leaving a gap between the lead bar and the functionally gradient material so that there is no contact between the two in the region where there is a large difference between their indices of thermal expansion. For example, this sort of seal using functionally gradient materials is described in Japanese Kokai Patent Publication HE1-115484 (1997).
The technology is to prevent cracking of the functionally gradient material due to a difference in indices of thermal expansion during operation of a lamp using a seal made of a functionally gradient material, by having no contact between the outer surface of the lead bar and the inner surface of the lead bar hole through the functionally gradient material. The structure described has a gap between the lead bar hole in the functionally gradient material and the lead bar itself.
Nevertheless, this technology is technology to prevent the occurrence of cracking during operation of the lamp; there is no consideration at all given to preventing the cracking that occurs during the post-sintering cooling stage of the process of manufacturing the functionally gradient material. Therefore there is no mention of the region of the functionally gradient material to which the lead bar is best attached, and that method cannot prevent the cracking which occurs during the process of manufacturing the functionally gradient material, which is the task of the invention of this application.
Other disclosures of the use of functionally gradient materials in lamp seals can be found in commonly owned, co-pending U.S. Pat. Nos. 6,107,740; 6,271,627 and 6,175,188.
It is an object of this invention to provide a lamp seal that avoids cracking of the functionally gradient material in the manufacturing process, and thus, assures that the finished product has adequate mechanical strength. Moreover, it is desired to provide a lamp seal with improved productivity when the light-emitting tube of the lamp is sealed by improving the case with which welding can be performed.
In order to achieve this object invention provides a lamp seal comprising a functionally gradient material and a lead bar, in which the functionally gradient material has layers of mixtures of electrically non-conductive material and conductive material such that one end is non-conductive and the other end is conductive, the proportion of conductive material in the layers increasing in stages or continually moving from one end to the other, in which the lead bar passes through a hole formed in the direction of layering of the functionally gradient material and is attached in the conductive region of the functionally gradient material, and in which the proportion of conductive material at the point of attachment of the lead bar to the non-conductive end of the functionally gradient material is no less than 0.6 Vol % and no more than 39 Vol %.
In accordance with the invention, the hole is cylindrical but has a larger diameter at the non-conductive end, such that, when C is the inside diameter of the cylindrical hole, d is the outside diameter of the hole and D is the outside diameter of the functionally gradient material, in the region from the non-conductive end of the functionally gradient material to the point of attachment of the lead rod, the inside diameter C satisfies the condition 1.2 dxe2x89xa6Cxe2x89xa60.6D.
Alternatively, the hole can expand in tapered form from the point of attachment toward the non-conductive end, with the thickness of the functionally gradient material from the point of attachment to the non-conductive end being less than its thickness at the point of attachment.
Moreover, in some embodiment, the outside diameter of the functionally gradient material at and near the non-conductive end is smaller than the outside diameter at the point of attachment.
The invention of this application is one which prescribes the region where the lead bar should be attached to functionally gradient material that has a layered structure with variation in the proportion of the conductive component. Specifically, the hole which allows the lead bar to pass through the functionally gradient material is divided into two regions; in one region the lead bar is attached to the functionally gradient material where the proportion of the conductive material is at a specified level, and in the other region there is a gap between the lead rod and the functionally gradient material so that the two are not in contact.
If the gap between the lead bar insertion hole and the lead bar is too short along the length of the lead bar, or in other words, if the non-contact region is the smaller of the two, then the point of attachment of the lead bar and the functionally gradient material is in the region of a higher proportion of the non-conductive component. In the process of manufacturing, the functionally gradient material, therefore, cracking is liable to occur in the cooling stage following sintering. On the other hand, if the gap is too long along the length of the lead bar, or in other words, if the non-contact region is too much longer, there will be little mechanical strength at the point of attachment of the lead bar and the functionally gradient material. For that reason, the seal material may break under pressure when it is fixed in place, or if the operator mistakenly touches the functionally gradient material.
The relationship between the inner diameter of the lead bar insertion hole and the outer diameter of the lead bar is explained next.
First, if the inner diameter of the lead bar insertion hole is too small, and the gap between the lead bar and the functionally gradient material is too narrow, during sintering in the process of manufacturing the functionally gradient material, the functionally gradient material will contract greatly, and at the same time, the lead bar inserted in the hole will undergo thermal expansion, so that the functionally gradient material will contact the lead bar in the region of a high proportion of the non-conductive material, and cracking will occur. And if the inner diameter of the lead bar insertion hole is too large, the wall of functionally gradient material will be too thin and handling during the production process prior to sintering will be difficult, resulting in breakage of the functionally gradient material. Moreover, even after the seal piece is created, deformation of a seal that is too thin during the subsequent process of manufacturing, such as when the silica light-emitting tube of the lamp is sealed by welding, would lead to problems in the manufacturing process.
If the diameter of the lead insertion hole is too large, on the other hand, and the wall of the seal is too thin, the thermal capacity of the seal will be reduced, and there will be problems in that the seal of the light-emitting tube will not be completely sealed.
The invention of this application provides a highly reliable lamp seal in which the proportion of conductive material at the point of attachment of the lead bar to the non-conductive end of the functionally gradient material is no less than 0.6 Vol %, which will prevent cracking of the functionally gradient material even during cooling after sintering, and is no more than 39 Vol %, which will facilitate handling of the functionally gradient material during the manufacturing process and will provide adequate mechanical strength in the finished product.
The use, according to the invention, of a hole formed in the direction of layering of the functionally gradient material which is a cylindrical hole with an expanded section will prevent contact with the internal surface of the functionally gradient material even during thermal expansion of the lead bar, if the hole""s inside diameter C is greater than 1.2 d, where d is the outside diameter of the hole. Furthermore, if the hole""s inside diameter C is less than 0.6D, where D is the outside diameter of the functionally gradient material, that will prevent breakage during manufacturing and also deformation of the seal piece when the light-emitting tube is sealed.
The third and fourth embodiments of this application facilitate seal processing and give final form to the sealing operation.
These and further objects, features and advantages of the present invention will become apparent from the following description when taken in connection with the accompanying drawings which, for purposes of illustration only, show several embodiments in accordance with the present invention.